$thickness : 5px;
$duration : 2500;
$delay : $duration/6;

@mixin polka($size, $dot, $base, $accent){
  background: $base;
  background-image: radial-gradient($accent $dot, transparent 0);
  background-size:$size $size;
  background-position: 0 -2.5px;
}

body {
  background-color: #1e6cc7;
  width: 100%;
  height: 100vh;
  margin: 0;
}

.bookshelf_wrapper {
  position: relative;
  top: 60%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.books_list {
  margin: 0 auto;
  width: 300px;
  padding: 0;
}

.book_item {
  position: absolute;
  top: -120px;
  box-sizing: border-box;
  list-style: none;
  width: 40px;
  height: 120px;
  opacity: 0;
  background-color: #1e6cc7;
  border: $thickness solid white;
  transform-origin: bottom left;
  transform: translateX(300px);
  animation: travel #{$duration}ms linear infinite;
  
  &.first {
    top: -140px;
    height: 140px;
    
    &:before,
    &:after {
      content:'';
      position: absolute;
      top: 10px;
      left: 0;
      width: 100%;
      height: $thickness;
      background-color: white;
    }

    &:after {
      top: initial;
      bottom: 10px;
    }
  }
  
  &.second,
  &.fifth {
    &:before,
    &:after {
      box-sizing: border-box;
      content:'';
      position: absolute;
      top: 10px;
      left: 0;
      width: 100%;
      height: $thickness*3.5;
      border-top: $thickness solid white;
      border-bottom: $thickness solid white;
    }

    &:after {
      top: initial;
      bottom: 10px;
    }
  }
  
  &.third {
    &:before,
    &:after {
      box-sizing: border-box;
      content:'';
      position: absolute;
      top: 10px;
      left: 9px;
      width: 12px;
      height: 12px;
      border-radius: 50%;
      border: $thickness solid white;
    }

    &:after {
      top: initial;
      bottom: 10px;
    }
  }
  
  &.fourth {
    top: -130px;
    height: 130px;
    
    &:before {
      box-sizing: border-box;
      content:'';
      position: absolute;
      top: 46px;
      left: 0;
      width: 100%;
      height: $thickness*3.5;
      border-top: $thickness solid white;
      border-bottom: $thickness solid white;
    }
  }
  
  &.fifth {
    top: -100px;
    height: 100px;
  }
  
  &.sixth {
    top: -140px;
    height: 140px;
    
    &:before {
      box-sizing: border-box;
      content:'';
      position: absolute;
      bottom: 31px;
      left: 0px;
      width: 100%;
      height: $thickness;
      background-color: white;
    }

    &:after {
      box-sizing: border-box;
      content:'';
      position: absolute;
      bottom: 10px;
      left: 9px;
      width: 12px;
      height: 12px;
      border-radius: 50%;
      border: $thickness solid white;
    }
  }
  
  &:nth-child(2) {
    animation-delay: #{$delay*1}ms;
  }
  
  &:nth-child(3) {
    animation-delay: #{$delay*2}ms;
  }
  
  &:nth-child(4) {
    animation-delay: #{$delay*3}ms;
  }
  
  &:nth-child(5) {
    animation-delay: #{$delay*4}ms;
  }
  
  &:nth-child(6) {
    animation-delay: #{$delay*5}ms;
  }
  
}

.shelf {
  width: 300px;
  height: $thickness;
  margin: 0 auto;
  background-color: white;
  position: relative;
  
  &:before,
  &:after {
    content:'';
    position : absolute;
    width: 100%;
    height: 100%;
    @include polka(10px, 30%, #1e6cc7, rgba(255,255,255,0.5));
    top: 200%;
    left: 5%;
    animation: move #{$duration/10}ms linear infinite;
  }
  
  &:after {
    top: 400%;
    left: 7.5%;
  }
  
}

@keyframes move {
  
  from {
    background-position-x: 0;
  }
  
  to {
    background-position-x: 10px;
  }
  
}

@keyframes travel {
  
  0% {
    opacity: 0;
    transform: translateX(300px) rotateZ(0deg) scaleY(1);
  }
  
  6.5% {
    transform: translateX(279.5px) rotateZ(0deg) scaleY(1.1);
  }
  
  8.8% {
    transform: translateX(273.6px) rotateZ(0deg) scaleY(1);
  }
  
  10% {
    opacity: 1;
    transform: translateX(270px) rotateZ(0deg);
  }
  
  17.6% {
    transform: translateX(247.2px) rotateZ(-30deg);
  }
  
  45% {
    transform: translateX(165px) rotateZ(-30deg);
  }
  
  49.5% {
    transform: translateX(151.5px) rotateZ(-45deg);
  }
  
  61.5% {
    transform: translateX(115.5px) rotateZ(-45deg);
  }
  
  67% {
    transform: translateX(99px) rotateZ(-60deg);
  }
  
  76% {
    transform: translateX(72px) rotateZ(-60deg);
  }
  
  83.5% {
    opacity: 1;
    transform: translateX(49.5px) rotateZ(-90deg);
  }
  
  90% {
    opacity: 0;
  }
  
  100% {
    opacity: 0;
    transform: translateX(0px) rotateZ(-90deg);
  }
  
}